I sincerely hope that the blood stops flowing and that the country emerges from the crisis through a phase of constructive transition that guarantees Syria its unity, stability and security, as well as the aspirations of its people. I am ready like any other Syrian, with no other ambition, to fulfil my civic duty to contribute to a better future for my country, as much as I can, and like all those … who have already made many sacrifices.

Qaboon saw some of the worst violence yesterday. The activist group, the Syrian Revolution General Commission, said government forces began shelling the area and attacking it with helicopters after sealing it off.

9.47am:Syria: More than 50 members of the regular army, including two colonels have been killed in fighting in the Damascus over the last two days, according to the British-based Syrian Observatory for Human Rights.

The Observatory's Rami Abdulrahman told the Guardian that the information was based on conversations with three doctors from two military hospitals in Damascus.

"The news is confirmed today by three doctors," he said.

One injured officer questioned why the Syrian media had stopped releasing information about military deaths, one of the doctors said, according to Abdulrahman.

Around 12 rebels were killed yesterday, Abdulrahman claimed, including three in Douma and seven in Qaboon.

He claimed deaths among regular troops outnumbered rebel casualties because of the hit and run tactics used by rebels. He said rebels had used RPGs to attack army vehicles carrying many troops, and then went into hiding.

Update:

The Dutch journalist Sander van Hoorn provides partial corroboration about military deaths after visiting one military hospital in Damascus.

Also visited military hospital. They had 34 soldiers there that died yesterday. Hospital (1200 beds) operating at full capacity #Syria

Le Figaro quotes an unnamed defence ministry source as saying: "Ballistic analysis and information gathered on site by our sources just after the incident indicate that Jacquier was killed by 81mm mortar shellfire coming from a Sunni rebel neighbourhood ... Analyses show quite accurately the source of the shot."

It adds that according to the source "all specialised services (DGSE and DCRI particular, NDLR) are in agreement on this conclusion".

10.09am:Syria: Reuters is reporting another suicide bombing in Damascus, citing state TV.

FLASH: Suicide bombing at national security building in Damascus - Syrian state television

10.37am:Syria: The journalist Zaid Benjamin, who claims to have been the first to report the start of the rebels' "operation volcano" assault, now says the Free Syrian Army is discussing withdrawing from Damascus.

The Free Syrian Army is discussing to halt #Damascus operations "Logistics supply lines are too long and out weapon capacity is limited"

11.38am:Syria: The defence minister, Gen Dawoud Rajha, was a Greek Orthodox Christian from Damascus. Aged 65, he was appointed defence minister last August. He had previously served as the army's chief of staff.

He was reportedly present at another high-level meeting in May where the rebel sources claimed to have poisoned several of those attending.

Assad has taken charge of a military crisis unit and takes all the daily decisions, from the deployment of army units to tasks assigned to the security services, as well as mobilisation of the Alawite Shabbiha, the feared militia accused of a series of massacres in the past two months.

"Bashar remains the centre. He is involved in the day-to-day details of managing the crisis," said a Lebanese politician close to the Syrian rulers. "He set up an elite unit led by him to manage the crisis daily."

In this unit, intelligence chief Hisham Bekhtyar is responsible for security coordination, Dawoud Rajha is minister of defence, Assef Shawkat, the president's powerful brother-in-law, is deputy chief of staff of the armed forces. Alongside them are Ali Mamlouk, special adviser on security, Abdel-Fattah Qudsiyeh, head of military intelligence, and Mohammad Nassif Kheyrbek, a veteran operator from the era of Assad's father.

Maher al-Assad, the president's younger brother and Syria's second most powerful man, commands the main loyalist strike forces.

11.42am:Syria: The Lebanese Hezbollah TV channel says the interior minister and Assad's brother-in-law have been wounded.

He says the way the state media has covered the attack is unprecedented. Speaking before the state media confirmed the death of Assef Shawkat, he said:

The reaction of state media is the biggest question here. Typically this isn't the kind of thing they announce. They like to give the impression that all is fine.

They didn't say it was a body guard. They said it was a suicide bomber who targeted the building, and the [only] casualty was Dawoud Rajha. State media hasn't elaborated on other casualties.

Asked to comment on speculation that the killing of the defence minister was a targeted to eliminate a potential defector Jabri said:

I'm not sure. They could have done it a lot more quietly. What they did today was create a media circus.

It could have been an internal elimination ... nobody is reporting a loud explosion. My theory is that it wasn't an internal thing, it was the FSA or some third party group - one of those groups who have snuck into Syria. From what I've heard so far I suspect it was an IED, because a suicide bomber would have had to dive into the building and exploded themselves inside it. You would ask how the hell the would he get in the building?'

This is a big development. It is likely to be used as an excuse to escalate the oppression campaign in Damascus. So I expect that by nightfall there is going to be a massive retaliation against the FSA in Damascus.

Hezbollah's TV station now says four top officials were killed: defence minister Dawoud Rajha, Assad's brother-in-law Assef Shawkat, interior minister Mohammad Ibrahim al-Shaar, and the head of the national security office.

Syrian TV has confirmed the deaths of Rajha and Shawkat.

Al-Jazeera also says the explosion in the meeting room was followed by gunfire.

1.06pm: News is breaking rapidly, but here's a summary of what we know so far:

• Syrian state television has announced the death of two key members of President Bashar al-Assad inner circle in a terrorist bomb attack against the national security building in Damascus. The blast killed defence minister Dawoud Rajha and his deputy Assef Shawkat - Assad's brother-in-law.

• Two groups have claimed responsibility for the explosions. Liwa al-Islam, an Islamist rebel group whose name means "The Brigade of Islam", said in a statement on its Facebook page that it "targeted the cell called the crisis control room in the capital of Damascus." The Free Syrian Army also claimed responsibility for the attack, according to spokesman Qassim Saadedine. "This is the volcano we talked about, we have just started," he said. Security sources have blamed the attack on a bodyguard for the regime's inner circle, according to Reuters.

• Several officials were also wounded in the attack, including intelligence chief Hisham Bekhtyar and the interior minister Mohammad Ibrahim al-Shaar. The blast occurred during a meeting of cabinet ministers and security officials, according to state TV.

• The Syrian government has vowed to wipe out those responsible, amid fears of increased bombardment against opposition strongholds. In a statement issued by the military it blamed the attack on "hired hands". It said it was "more determined than ever to confront all forms of terrorism and chop any hand that harms national security".

1.56pm:Syria: Britain's foreign secretary, William Hague, has condemned today's attack in Damascus, saying it "confirms the urgent need for a chapter VII resolution of the UN security council", the Press Association reports. He continued:

The situation in Syria is clearly deteriorating. All the members of the UN security council have a responsibility to put their weight behind the enforcement of joint special envoy Kofi Annan's plan to end the violence.

We call on all parties to refrain from violence and for the Security Council to shoulder its responsibilities.

A chapter VII resolution would increase pressure on the Assad regime.

Former foreign minister Lord Malloch-Brown, speaking on BBC Radio 4, said today's attack was "an astonishing penetration of Syrian security", adding: "It will be a huge blow to their morale."

2.03pm:Syria: Several tweets claim that the first vice-president, Farouk al-Sharaa, has defected to Jordan. At present we have no reason to believe these are anything more than rumours. We're awaiting confirmation – or not.

I arrived Midan with a friend at 12:30 PM today 18-7-2012, there was a shooting very close to us but we managed to arrive safely. I cannot share my location with you in Midan, nor can I say who's with me here. We are safe so far.

Clashes started early in the morning and it's still on, we sometimes hear explosions every now and then, the residents of area here are telling us there are BMB tanks shelling the center of the area.

There are several checkpoints in the area, but the area we're in right now is relatively safe thus far, there are four people martyred today in Midan alone; 3 from Free Syrian Army and the fourth is a civilian- an old man we couldn't find his ID with him, we're in the process of getting his name.

2.25pm:Syria: The former defence minister and current assistant vice president, Hassan Turkmani, was also killed in the blast according to Reuters, citing a pro-government TV channel.

5.25pm: Reuters reports that a UN vote on whether the mandate of its monitoring force in Syria should be extended – due to take place later today in New York – has been cancelled.

Mohammad Ibrahim al-Shaar

Reports differ on the fate of the interior minister.

State TV reported that he had been killed.

The pro-government channel Dounia, denied that he was dead. It reported that he is in a stable condition.

Hassan Turkmani

The former defence minister and was known as the the regime's crisis management chief.

Until his death Turkmani was serving as an assistant to the country's vice president. In his mid-70s, Turkmani was close to the regime and took part in the crackdown against the uprising. Shortly after the revolt began in March last year, Assad sent Turkmani to Turkey for talks with officials there.

Shawkat, married to Assad's sister Bushra, was one of the most feared figures in the president's inner circle and had won the support of the clan's influential matriarch, Anisa. He was one of three central figures in the regime crackdown, along with Assad himself and his brother Maher. As Syria's overall security chief, he had key input into all military and intelligence operations. He is known to have survived an attempt to poison him in late May when a cook contaminated food that had been prepared for him and key members of the national security ministry.

As is the case in many ministries, there was an Alawite, President Bashar al-Assad's brother-in-law Assef Shawkat, in the number two position at defence, and his membership of the family network was far more important than title.

Furthermore, the defence ministry is less powerful than the interior ministry, intelligence service and Maher al-Assad's Republican Guard. But Rajha's presence around the table at the national security council reflected the fact that he wielded real clout in the apparatus.

• Four senior members of the Bashar al-Assad's inner circle have been killed in a bomb attack on the national security building in Damascus, in what amounts to a grave crisis for the ruling regime. The blast killed defence minister Dawoud Rajha and his deputy Assef Shawkat - Assad's brother-in-law. Also killer were the interior minister Mohammad Shaar and the assistant vice president, Hassan Turkmani. The blast occurred during a meeting of cabinet ministers and security officials, according to state TV.

• Two groups have claimed responsibility for the explosions. Liwa al-Islam, an Islamist rebel group whose name means "The Brigade of Islam", said on its Facebook page that it "targeted the cell called the crisis control room in the capital of Damascus." The Free Syrian Army also claimed responsibility for the attack, according to spokesman Qassim Saadedine. "This is the volcano we talked about, we have just started," he said. Security sources have blamed the attack on a bodyguard for the regime's inner circle, according to Reuters.

• The US defence secretary, Leon Panetta, says the situation in Syria is "spiralling out of control". He called on the international community to "bring maximum pressure on Assad to do what's right to step down and allow for that peaceful transition" The Russian foreign minister, Sergei Lavrov says a "decisive battle" is under way in Syria. A UN vote on the future of its monitoring force in Syria, due to take place today, has been cancelled.

• The Syrian government has vowed to wipe out those responsible for the blast, amid fears of increased bombardment against opposition strongholds. In a statement issued by the military it blamed the attack on "hired hands". It said it was "more determined than ever to confront all forms of terrorism and chop any hand that harms national security".